I have used qemu-img for converting vmdk images to qcow2 in the past. It works on Virt-Manager, at least it did for me when I ran Fedora Workstation. On Silverblue, I can get the image to work in Boxes, but not with Virt-Manager layered. In boxes, I can use normal USB connected things like thumb drives and keyboards/mice/tablets, but not communication devices since they don’t get mapped to /proc/bus/usb but to /dev/bus/usb. That leaves the software I need functional, but only partially since I cannot connect to external devices to download the programs I write for them. In the VM I can see the offending device as a pci device, that I cannot load a driver for. I do have the spice guest tools installed, did that first, then updates, then installed the desired programming software. Since I did accomplish this very thing as recently as F27 on workstation with Virt-Manager, I can only guess that it is due to Silverblue’s file system layout and how it handles usb networking, possibly the spice virtio stuff is not getting what it needs.